Questions: hello@norea.studio
Because no archaeological date is exact. Palimpsest cannot store a date without an uncertainty — the type refuses a zero. The band beside the date is that uncertainty drawn on the same axis as the other layers of the same place, so you can compare them at a glance.
A filled circle means measured: an excavation report and a date. A half circle means reconstruction: a published interpretation with broad acceptance. An empty ring means disputed: the same evidence is read in more than one way, and we say so instead of picking a side. The marks are shapes rather than colours so that they still work if you do not see colour.
Göbekli Tepe, Nabta Playa and Çatalhöyük all have published alignment claims, but the claims contradict one another. Writing down one of them as a number would make it look like a measurement. Those places are stored without an orientation, and the app tells you that is why.
No, and the screen says so. It is computed from the obliquity of the ecliptic for that site's latitude and that layer's epoch. Where a field survey exists it is drawn as a solid line next to the dashed computed one, and the app states whether the survey supports the claim. Where the epoch falls outside the published obliquity range, the figure is an extrapolation and is shown without animation.
Equal steps give every layer the same share of the slider: easy to navigate, but it teaches a false sense of scale. Proportional spacing is true to the years but can leave a modern layer as a sliver. Neither is more correct, so the setting is yours — and either way the real gap in years is written under the slider.
It only works offline, in the sense that it never goes online. Everything is compiled into the app before it ships. There is nothing to sync and nothing to wait for, in a museum basement or on a plane.
The watch app answers one question: what stood here? Turn the Digital Crown to move through a place's layers. The source list and the alignment arc are on iPhone and iPad — nobody reads a bibliography on a wrist.
If a date, a source or an azimuth looks wrong to you, please write. A correction with a citation is the most useful message this app can receive, and it goes into the catalogue with your source recorded beside it.